Treatment of knitted fabrics



KR EQQYYrETI 3,077,371 TREATMENT OF KNITTED FABRICS Werner A. P. Schoeneberg, Murray Hill, and Fred Fortess,

New Providence, N..l., assignors to Celanese Corporation of America, New York, N.Y., a corporation of Delaware No Drawing. Filed Feb. 14, 1956, Ser. No. 565,311

6 Claims. (Cl. 8-107) This invention relates to the treatment of knitted fabrics and relates more particularly to the treatment of knitted fabrics having a basis of a cellulose ester of low hydroxyl content.

It is an object of this invention to provide a new and improved process for the production of dimensionally stable knitted fabrics.

Another object of this invention is the provision of a novel method of treating knitted fabrics having a basis of a cellulose ester of low hydroxyl content to improve their dimensional stability and to produce a fabric of good white color.

Other objects of this invention will be apparent from the following detailed description and claims. In this description and claims all proportions are by weight unless otherwise indicated.

In accordance with one aspect of this invention, a knitted fabric having a basis of fibers of a cellulose ester of low hydroxyl content is treated by a procedure which involves bleaching of the fabric in aqueous medium and, before completion of said bleaching, i.e. prior to or during said bleaching, subjecting the fabric to an aqueous liquid under superatmospheric pressure and at a temperature of at least about 250 F.

The cellulose esters of low hydroxyl content employed in the process of this invention contain not more than 0.29, preferably 0.0 to 0.12, alcoholic hydroxyl groups per anhydroglucose unit in the cellulose molecules thereof. Best results are obtained by the use of cellulose acetate of low hydroxyl content and of correspondingly high acetyl value, e.g. an acetyl value of at least 59%, preferably 61 to 62.5%, calculated as combined acetic acid. However, other lower aliphatic acid esters of cellulose of low hydroxyl content may be employed. Examples of such esters are cellulose-propionate, cellulose butyrate, cellulose acetate-propionate, cellulose acetate-butyrate and cellulose acetate-formats.

It is preferred to scour the knitted fabric, before the bleaching treatment, in order to remove any foreign materials such as sizes and yarn lubricants. For best results the scouring is carried out in an aqueous liquid at a relatively high temperature of at least about 250 F. and at a superatmospheric pressure sufliciently high to maintain the scouring medium in the liquid state at this temperature. Thus, for example, temperatures of about 250 to 280 F. and pressures of about 12 to 30 p.s.i.g. may be used. This high temperature treatment under pressure has the added effect of stabilizing the knitted fabric so that it will not tend to shrink or change its shape substantially on subsequent Washing. Preferably during the high temperature scouring the fabric is maintained at substantially constant dimensions by suitable mechanical means. To effect a high degree of stabilization the high temperature scouring should be continued for at least about 60 minutes when the scouring temperature is 250 F. With higher scouring temperatures less time is needed to attain the same stabilization.

The aqueous liquid used in the scouring treatment may contain any of the usual scouring agents, such as soaps or synthetic detergents. A solution containing soap and a sequestering agent, such as sodium hexametaphosphate, yields excellent results. Other useful scouring agents are the sodium salt of oleyl taurate and combinations of transact "ice I sulfonated oils and nonionic detergents. The scouring solution generally contains at least of water.

For effecting the bleaching of the fabric any of the bleaching agents customarily employed in the art may be used. Thus, very good results have been obtained by the use of aqueous solutions of bleaching agents containing hydrogen peroxide, peracetic acid, oxalic acid, sodium hypochlorite, and sodium chlorite, taken alone or in various combinations. It is often desirable to incorporate into the bleaching solution a sequestering agent, such as sodium hexametaphosphate and also a dispersing agent, all in a manner well known to the art. When the bleaching agent is hydrogen peroxide it is advantageous to add thereto a stabilizer for the peroxide, e.g. sodium metasilicate; the pH of the resulting mixture preferably should not exceed about 9.5, since at higher pH values the cellulose ester may be unnecessarily saponified. Generally, the bleaching solution contains at least 95% of water. The bleaching treatment may be carried out at atmospheric, superatmospheric or even subatmospheric pressure.

When the fabric has previously been given a scouring treament at a sufficiently high temperature and for a sufficient length of time to stabilize the fabric dimensions and configuration, as described above, the bleaching treatment may be conducted at a lower temperature, i.e. a temperature below that used for scouring. Thus, in this case bleaching temperatures of, for example, 230 to 240" F. are suitable.

When there has been no preliminary scouring treatment or when the scouring treatment has not been such as to stabilize the fabric dimensions and configuration, the bleaching solution should be at a high temperature of at least about 250 F. and under a superatmospheric pressure sufficiently high to maintain the bleaching solution in its liquid state, e.g. a temperature of about 250 to 280 F. and a pressure of about 12 to 30 p.s.i.g. This high temperature bleaching results in stabilization of the size and shape of the fabric, and it is therefore desirable, during such bleaching, to maintain the fabric at constant dimensions by suitable mechanical means. The high temperature bleaching should be continued for a sufficient period of time to impart the desired dimensional stability to the fabric. Thus, about 30 to 60 minutes of bleaching at a temperature of about 250 to 260 F. has been found to give very good results. It will be understood, of course, that the fabric may be partially stabilized by a relatively short high temperature scour and that the stabilization may be completed during a high temperature bleaching treatment, which in this case need not be of such long duration as if there had been no previous partial stabilization of the fabric.

The process of this invention yields white fabrics having a high degree of dimensional stability and resistance to yellowing. In contrast, if the fabric is treated in another way, by first bleaching it in the usual manner and then subjecting it to steam under pressure in an autoclave to improve its dimensional stability, a yellowed fabric is obtained.

During the high temperature treatment of this invention a crystalline structure is developed in the cellulose ester of low hydroxyl content. Thus, in the case of cellulose acetate of low hydroxyl content the crystalline order index (as determined by study of the X-ray diffraction pattern, as described below) is increased to about 1.4 or higher. In addition, the safe ironing point of the cellulose acetate of low hydroxyl content is raised to about 250 C. (about 480 F.). The treatment improves the dimensional stability of the knitted fabric to such an extent that even after five washes in a conventional household washing machine at F. the fabric shrinks a total of less than 7% in area. It also improves states and to a significant extent the resistance of the fabric to wrinkling on washing.

The crystalline order index referred to above is obtained by calculation from curves based on X-ray dilfractometer studies of samples of the treated fabric. These curves are plots of intensity of the diffracted beam against the angle of the beam. Thus, the curve for cellulose triacetate has four pronounced peaks at angles of 8, 10, 12.6 and 16, the angle being that which the diffracted X-ray beam makes with respect to the incoming X-ray beam. The degree of heat treatment will affect the sharpness of these peaks. The crystalline order index, which is an indication of the sharpness of the peaks, is the average of the ratios of each peak height to its width at half height for the four peaks mentioned above. For producing the ditfractometer curves used for measuring the crystalline order index there is employed a North American Philips Geiger counter ditfractometer operated under the following conditions.

Radiation: Nickel filtered Cu Ka radiation 35 kv., 14 ma., using both voltage and ma. stabilization. Diffractometer constants: 3 take-off, 1 divergence slit; .003" receiving slit (0.025 1 scatter slit; 2 26/min. scanning speed. Recorder constants: Ratemeter, Scaler--8, Multiplier-0.6 (full scale 240 counts/sec). Time constant: 16. Chart speed: 0.5/min.

As stated, it is desirable to maintain the fabric at constant dimensions during treatment. In one suitable arrangement the fabric is wound, in flat unfolded condition, on a perforated tubular metal beam, and the resulting roll is placed into an appropriate pressure-tight apparatus where treating fluid under pressure is circulated through the roll of fabric, the fluid passing through the perforations in the beam. In order to prevent widthwise shrinkage of the fabric during treatment, the selvedges of the fabric are held in place by taping them or by introducing a suitable binding cord onto the selvedges as the fabric is wound onto the beam. To further restrain movement of the fabric the entire roll is wrapped with cotton fabric and, finally, with a girdle of steel mesh before the roll is placed in the treating apparatus.

In order to avoid stressing the fabric unduly after the treatment of this invention and thus introducing strains which may have an effect on the dimensional stability of the knitted fabric, the treated material should be maintained in a relaxed condition during subsequent drying and finishing operations.

The following examples are given to illustrate this invention further.

Example I A tricot fabric warp-knitted of yarns composed of continuous filaments of cellulose acetate of an acetyl value of 61.7% calculated as combined acetic acid, and having 76 courses per inch and 28 wales per inch, is scoured for 30 minutes at a temperature of 250 F. and under a pressure of 15 p.s.i.g. with an aqueous solution containing 1 gram per liter of Calgon" (sodium hexametaphosphate) and 1 gram per liter of soap (sodium oleate). Thereafter, the scoured fabric is rinsed twice with water and then bleached for one hour with an aqueous solution hav ing a pH of 6.5 and containing 2.3 grams per liter of peracetic acid, 0.85 gram per liter of caustic soda and 0.5 gram per liter of Calgon at a temperature of 260 F. and a pressure of p.s.ig During the entire process the fabric is held at constant dimensions. The resulting fabric has excellent dimensional stability and a high degree of whiteness, and shows very little tendency to yellow when exposed to sunlight or nitrogen oxides. It has little tendency to become wrinkled when washed.

Example II A fabric as described in Example I is scoured for one hour at a temperature of 270 F. and under a pressure of 27 p.s.i.g. with an aqueous solution containing 2% of Calsolene oil HS (a highly sulfonated oil), 1% of Triton X-l00 (an alkyl aryl polyoxyethylene ether alcohol) and 0.5% of soda ash, and having a pH of 8.5. The fabric is then rinsed and thereafter bleached at a temperature of 230 F. for 1 hour at a pressure of 6 p.s.i.g. with an aqueous solution containing 4.7 grams per gallon of peracetic acid, 1.6 grams per gallon of soda ash, 1.4 grams per gallon of Calgon and 0.2 gram per gallon of Igepon T-77 (sodium salt of oleyl taurate), and having a pH of 6.5. Thereafter the fabric is rinsed thoroughly. During the entire process the fabric is held at constant dimensions. The resulting fabric has excellent dimensional stability, a high degree of whiteness and shows very little tendency to yellow on exposure to sunlight or nitrogen oxides. It has little tendency to become wrinkled on washing.

Example III Example II is repeated except that, after the scouring and rinsing, hot Water is circulated through the fabric. 1 gram per liter of oxalic acid is added to this circulating water at F., the water temperature is then raised to F. and there are added to the circulating water 0.5 cc. per liter of 35% hydrogen peroxide, 1 gram per liter of Textone (sodium chlorite) and 1 gram per liter of X-Tan-Assist (a bleaching assistant made by Tanatex Corporation for preventing odor formation and for inhibiting corrosion of the stainless steel vessel used in the treatment) to form a solution having a pH of 3 to 4. The temperature is then raised to 230 F. and the fabric is subjected to the solution for 1 hour at a pressure of 6 p.s.i.g. The resulting bleached fabric is rinsed and then treated for 20 minutes at a temperature of 160 F. with an aqueous solution containing 0.25 gram per liter of Igepon T-77 and 1 gram per liter of tetrasodium pyrophosphate. The fabric is maintained at constant dimensions throughout the treatment. The properties of the fabric are similar to those of Example II.

It is to be understood that the foregoing detailed description is merely given by way of illustration and that many variations may be made therein without departing from the spirit of our invention.

Having described our invention, What We desire to secure by Letters Patent is:

1. Process for the treatment of fabrics, which comprises bleaching at a pH which does not exceed about 9.5 a knitted fabric comprising fibers of a cellulose lower aliphatic acid ester containing at most 0.29 free OH groups per anhydroglucose unit the remaining groups being cellulose ester groups such that most of said anhydroglucose units contain three ester groups, and during said bleaching subjecting said fabric to an aqueous liquid at a temperature of at least 250 F. but below the melting point of the fabric for a time sutficient to obtain a cellulose ester fabric of improved dimensional stability.

2. Process for the treatment of fabrics, which comprises bleaching at a pH which does not exceed about 9.5 a knitted fabric comprising fibers of cellulose acetate of at least 61% acetyl content, calculated as combined acetic acid such that most of the anhydroglucose units of said cellulose acetate contain three acetate groups, and during said bleaching subjecting said fabric to an aqueous liquid at a temperature of at least 250 F. to obtain a cellulose acetate fabric of improved dimensional stability.

3. Process as set forth in claim 2 in which said fabric is held to constant dimensions while it is subjected to said aqueous liquid.

4. Process for the treatment of fabrics, which comprises scouring a warp-knitted tricot fabric comprising fibers of cellulose acetate of at least 61% acetyl content, calculated as combined acetic acid, such that most of the anhydroglucose units of said cellulose acetate contain three acetate groups, said scouring taking place in an aqueous liquid containing a scouring agent at a temperature of at least 250 F. but below the melting point of the fabric and under superatmospheric pressure and then bleaching said fabric at a pH not exceeding about 9.5

to obtain a cellulose acetate fabric of improved dimen sional stability.

5. Process as set forth in claim 4 in which the bleaching is carried out at a temperature lower than that used for the scouring.

6. Process for the treatment of fabrics which comprises subjecting a knitted fabric comprising fibers of a cellulose lower aliphatic acid ester to an aqueous liquid at a temperature of at least 250 F. but below the melting point 10 of the fabric and under superatmospheric pressure, said cellulose ester containing at most 0.29 free OH group per anhydroglucose unit, the remaining groups being cellulose ester groups, such that most of said anhydroglucose units contain three ester groups, and then bleaching said fabric at a pH not exceeding about 9.5 to obtain a cellulose ester fabric of improved dimensional stability.

References Cited in the file of this patent UNITED STATES PATENTS 2,303,934 Heckert Dec. 1, 1942 2,313,173 Schneider Mar. 9, 1943 2,365,931 Benger Dec. 26, 1944 2,499,142 Helmus Feb. 28, 1950 2,563,394 Cadgene Aug. 7, 1951 2,669,502 Walmsley Feb. 16, 1954 2,684,360 Davoud July 20, 1954 2,750,781 Bailey June 19, 1956 2,862,785 Finlayson Dec. 2, 1958 OTHER REFERENCES Fortess: American Dyestuff Reporter, Aug. 1, 1955, pages P524-P537.

Boulton: Jour. of the Soc. of Dyers and Colorists, August 1955, pages 451-464.

Textile Manufacturer, February 1955, pages 71 and 72.

Baker: Journal of the American Chemical Society, April 1942, vol. 64, pages 776-782. 

1. PROCESS FOR THE TREATMENT OF FABRICS, WHICH COMPRISES BLEACHING AT A PH WHICH DOES NOT EXCEED ABOUT 9.5 A KNITTED FABRIC COMPRISING FIBERS OF A CELLULOSE LOWER ALIPHATIC ACID ESTER CONTAINING AT MOST 0.29 FREE OH GROUPS PER ANHYDROGLUCOSE UNIT THE REMAINING GROUPS BEING CELLULOSE ESTER GROUPS SUCH THAT MOST OF SAID ANHYDROGLUCOSE UNITS CONTAIN THREE ESTER GROUPS, AND DURING SAID BLEACHING SUBJECTING SAID FABRIC TO AN AQUEOUS LIQUID AT A TEMPERATURE OF AT LEAST 250* F. BUT BELOW THE MELTING POINT OF THE FABRIC OF IMPROVED DIMENSIONAL STABILITY. A CELLULOSE ESTER FABRIC OF IMPROVED DIMENSIONAL STABILITY,
 6. PROCESS FOR THE TREATMENT OF FABRICS WHICH COMPRISES SUBJECTING A KNITTED FABRIC COMPRISING FIBERS OF A CELLULOSE LOWER ALIPHATIC ACID ESTER TO AN AQUEOUS LIQUID AT A TEMPPERATURE OF AT LEAST 250* F. BUT BELOW THE MELTING POINT OF THE FABRIC AND UNDER SUPERATMOSPHERIC PRESSURE, SAID CELLULOSE ESTER CONTAINING AT MOST 0.29 FREE OH GROUP PER ANHYDROGLUCOSE UNIT, THE REMAINING GROUPS BEING CELLULOSE ESTER GROUPS, SUCH THAT MOST OF SAID ANHYDROGLUCOSE UNITS CONTAIN THREE ESTER GROUPS, AND THEN BLEACHING SAID FABRIC AT A PH NOT EXCEEDING ABOUT 9.5 TO OBTAIN A CELLULOSE ESTER FABRIC OF IMPROVED DIMENSIONAL STABILITY. 